This question has been raised often on this forum, so there's really little to add. But I'll try.
First, by way of recycling a remark someone made some time ago. Until the early 20th century, science had identified four distinct taste receptors, and so four distinct tastes: salt, sweet, bitter and sour. Then a Japanese researcher identified a fifth: umami (savory). Did we taste this flavor before receptors for it were discovered by science? Undoubtedly we did. Lesson: the question of what can be "measured" depends on the state of the relevant science--and, as hilde45 (the OP) suggests a few comments above, science is continually expanding the horizons of our understanding.
That said, I remain a skeptic regarding the underlying assumptions of many of our passionate convictions as audiophiles. How our brains process sound is such a complex matter that it seems to me essentially a fetish to place so much emphasis on any single feature, especially when that feature is of marginal impact. It's not even fair to appeal to A/B/X blind testing as the gold standard for answering such questions; I think we all know that, for many aspects of our quest for the Absolute Sound, sustained listening--not just over hours, but over days, weeks, years--is necessary. After all, a given individual's capacity for critical listening changes over time. Acuity of hearing diminishes with age while one's mental catalog of past experiences with music increases; emotional sensitivity is different at different times; physiological variables are relevant (degrees of relative health; the presence or absence of intoxicants--it's a long list); acoustics vary even with the weather in the same room. Most importantly, and not under the listener's control, the quality of the original recording (or the acoustics of the venue, if the musical experience is live) is the fundamental limiting factor on everything else. Cables and interconnects are one of these many variables, and not by any means (IMO) among the more important ones.
But we're all control freaks. And we all want to make improvements to our systems for as modest an additional investment as possible. Hence, we hope to burnish our already shiny toys with "tweaks." That's perfectly understandable, even laudable. But it's also a distraction. At some point, you've got to decide what you're in this game for: the technology, and its near-miraculous abilities, or the music? A quote attributed to Alan Parsons comes to mind: "Audiophiles don't use their equipment to listen you your music. Audiophiles use your music to listen to their equipment." That stings. Too often, I find myself choosing music because is well-recorded and sounds good on my system. If I'm honest, I'm inclined even to confess that my recent taste in "music" is partly determined by what sounds good on my system--even though I've lived with music all my life, I play several instruments, my wife and daughter are accomplished musicians. That's ass backwards.
